Natural gas is an environment-friendly and highly calorific source of energy. The whole process of gas extraction and transport adheres to strict environment protection rules, and minimum levels of noxious pollutants are emitted in its combustion.

International environment protection organizations and governments raise a clamour and demand that environment pollution be limited by reducing the amount of noxious compounds and volatile substances discharged into the air. Such measures increase the popularity of natural gas as the cleanest energy carrier amongst natural fuels.

Methane is a natural fossil fuel. It was formed, not unlike crude oil, in chemical processes changing the remains of plants and animals into hydrocarbons. It occurs naturally together with oil deposits (wet gas) or separately (dry gas).

The composition of natural gas and its content vary depending on the place of extraction, but its key component is methane and it always exceeds 90% of natural gas. Apart from methane, there may be small amounts of ethane C2H6, propane C3H8, butane C4H10 and other organic and mineral compounds.

Natural gas is:

• lighter than air
• colourless
• odourless

Because of its odourless nature, before natural gas is delivered to the user it is mixed with tetrahydrothiophene, which gives it a specific odour. This enables one to smell natural gas in the event of uncontrolled gas leakage.

On top of the fact that natural gas is not an environmental nuisance (its burning does not discharge sulphur dioxides or nitrogen dioxides) it is also very convenient for the user (no ash or soot). Other values of natural gas include the ease and convenience of transport, easiness to control and automate the combustion process and, what is most import from the cost perspective, a possibility to achieve higher rates of energy efficiency compared to devices fueled by other energy carriers.

Liquid gas means: propane, butane, propylene, butene, methane, ethane and pentane. These are gases that become liquid at ambient temperatures and low pressure. Other market names can also be met, i.e. propane-butane.

The most popular forms are: propane, butane, the mixture of propane and butane with a small addition of other gases. Liquid gas is stored and transported in cylinders or pressurised tanks.

Fuel type	Sales unit	Calorific value	Calorific value unit
Electric energy	1 kWh	3,6	MJ/kWh
Hard coal	1 kg	24,5-33,8	MJ/kg
Coke	1 kg	30,5	MJ/kg
furnace oil ECOTERM	1 kg 1 l	43,2 38,8	MJ/kg MJ/l
Petrol	1 kg 1 l	43,5 39,2	MJ/kg MJ/l
propane-butane (1:1) liquid phase propane-butane (1:1) liquid phase propane-butane (1:1) gas phase	1 kg 1 l 1 m3	46,0 25,1 106,9	MJ/kg MJ/l MJ/m3
propane liquid phase propane liquid phase propane gas phase	1 kg 1 l 1 m3	46,3 23,6 91,3	MJ/kg MJ/l MJ/m3
butane liquid phase butane liquid phase butane gas phase	1 kg 1 l 1 m3	45,6 26,4 122,6	MJ/kg MJ/l MJ/m3
natural gas (GZ-50) subgroup E	1 m3	35,4	MJ/m3